The present invention relates to a vehicle body with a curved metal plate floor.
The present invention relates particularly, although by no means exclusively, to a system for attaching a curved metal plate floor to a support frame of a load carrying body of a vehicle, such as a truck or a rail wagon.
The present invention is described hereinafter particularly in the context of trucks and truck bodies. However, it is emphasised that the present invention is not limited to trucks and truck bodies.
In most mining and quarrying applications, the floors of truck bodies are constructed of flat plates welded into the main structures of the bodies. In some more recent truck bodies, the floor plates are curved and welded into the main structures of the bodies.
The plate floors are welded to the sides of the body and to supporting beams on the underside of the floor plates. The floor plates are generally made from high strength abrasion resistant steels.
Mining truck bodies are typically very large. Payload capacities in excess of 100 tonnes are common and in the largest trucks, payloads are greater than 350 tonnes. During truck loading operations, loads up to about 100 tonnes may be dropped several meters directly onto the floor of the truck body.
The material loaded into mining or quarrying trucks may vary widely in nature, even in the one mine. In one application it may be mostly large, hard, sharp cornered and very abrasive rocks. In another application the payload material may consist of smaller and softer rocks that are very abrasive. In yet another application, the payload may have a high proportion of cohesive material that sticks to parts of the body and does not shed fully from the body during load tipping operations. Typically, a mining truck body and particularly the floor must be able to handle wide variations in rock impact, abrasive wear (mainly during the load tipping/dumping operations) and cohesiveness of the material carried.
Mining trucks are typically expected to have a working life of at least 60,000 operating hours and during this time a single truck could experience about 300,000 load-haul-dump cycles.
The thickness of the steel truck body floors are typically in the range of 16 to 50 mm.
Thicknesses greater than about 25 mm are typically made up of a base plate and a high hardness wear resistant steel plate welded on top of the base plate. The top plate may be selectively placed rather than uniform over the whole area of the floor. Sometimes, spaced apart bars are used to reduce abrasive wear of the floor plate. Furthermore, numerous large supporting beams are required under these floor plates. These beams are required to prevent excessive bulging type permanent deformation of the floor when large rocks are dropped onto it.
Replacement or substantial repair of a truck body floor is typically required at least twice during the operating life of a mining truck. This repair work generally necessitates exchange of the truck body with a new or repaired body or that the truck spend a lengthy time in a workshop. The repair of truck body floors is a significant cost item for many mining trucks.
In an effort to overcome the problems and costs associated with floors made from flat steel plates, the use of suspended rubber floors in truck bodies has also become established in the mining industry. In this case, the floor consists of a single thick piece of rubber or a double thickness of rubber sheeting supported by numerous cables spanning between beams at the base of the side sections of the body. The cables are made of multiple strands of steel or elastomeric material. The cables act to carry the vertical forces from the load in the body via tension in the cables similar to the way the cables of a suspension bridge carry the loads from the road section of a “suspension bridge”.
The main advantages of the suspended rubber floor are:                Moist clay containing cohesive materials are less likely to stick to the body when it is tipped to dump the load.        When worn out or badly damaged, the floor can be replaced relatively quickly.        The empty weight of the body is sometimes less than for an all steel body of equivalent capacity.        
The improved shedding of cohesive (sticky) materials mainly results from the flexing of the rubber floor during load tipping operations.
The disadvantages of the suspended rubber floor are:                The initial purchase cost is higher than for an all-steel truck body.        Frequent re-adjustment of the floor support cables is required (to adjust for permanent stretching that occurs).        Intermittent and un-predictable replacement of failed or severely damaged cables is required.        The rubber floor can be torn by large and sharp rocks.        Replacement floors are expensive.        
Because of the above difficulties, the applicant believes that the use of suspended rubber floors has been limited to less than 10% of all mining applications. Their use is mainly restricted to applications where the improved shedding of sticky materials is very important and/or where the elimination of supplementary wear resistant steel plating on the floor of the body is highly beneficial.
Analytical modelling work and mine site trials have shown that an alternative to the above-described floors is suspended curved metal (typically steel and hereinafter described in that context) truck body floors.
In any given application, a curved steel plate is supported only at the two sides of a truck body so that it curves down from and is suspended between the supporting points at the sides.
The suspended curved steel floor plate provides the general load containing function and acts as a tension member to transfer the vertical forces from the load on the floor to tension forces which are transferred into a support frame of the truck body. The support frame comprises beams at the base of the sides of the body. Because the suspended curved steel floor plate carries the forces arising from the payload primarily through tension forces within the plate, it has sometimes been referred to as a steel membrane floor. However, in practice the bending stiffness of the plate (arising from the thickness required to provide a long life against abrasive wear), the high variability in the placement of the loads carried, and in some cases, eccentricity of the load transfer points on the edges of the floor, means that the suspended curved steel floor plate is also subjected to moderate bending loads. Unless it is severely overloaded, the suspended curved steel floor plate experiences only small changes from its initial shape.
Several edge-supported curved steel plate floors have performed successfully in extended mine site trials during 1996 and 1997. These floor systems were for a large rear dump mining truck with a rated payload capacity of approximately 180 tonnes.
The applicant has invented a system that attaches a curved metal plate floor to a load carrying body of a vehicle, such as a truck or rail wagon. The system is described and claimed in Australian patent 2006228988 in the name of the applicant and the disclosure in the patent specification of the patent is incorporated herein by cross-reference. The system includes a series of tensile members that are connected directly or indirectly at opposite ends to (a) the floor plate and (b) the body of the vehicle and these tensile members are at least the principal means for transfer of forces from the floor plate to the body. The patent describes a particular form of the tensile members.
The above description is not to be taken to be an admission of the common general knowledge in Australia or elsewhere.